JPH0570576B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is a magnetic tape useful for producing a magnetic tape by forming a magnetic layer on the surface of a film by coating magnetic particles and a binder on the surface of the film or by a plating method. Base film and magnetic tape using the same. [Prior Art] Base films such as cellulose acetate and polyethylene terephthalate have traditionally been widely used as base films for magnetic recording media. With the increase in speed,
There is an increasing demand for such films to be extremely thin and have high dimensional stability. [Problems to be Solved by the Invention] In the case of magnetic tape, in order to further improve the running properties and image stability of the tape, it is necessary to use a base material that has particularly good Young's modulus and dimensional stability. If the Young's modulus of the base film is low, the magnetic tape will stretch due to excessive tension in the running direction, impairing image stability. This is a big problem with magnetic tapes based on thin films, and the most important problem is ensuring the Young's modulus in the running direction, that is, in the longitudinal direction. In addition, if the dimensional stability is poor, inconvenient problems such as skew and track deviation may occur due to environmental changes, which is undesirable. [Means for Solving the Problems] The present inventors have conducted intensive research to obtain a high-performance base film for magnetic tapes that satisfies such requirements, and as a result, the present inventors have developed biaxially oriented polyoxymethylene having certain physical properties. The inventors have discovered that an extremely excellent magnetic tape can be obtained by using a film as a base, and have arrived at the present invention. (Structure of the Invention) The present invention consists of the following structure. That is, it is a biaxially stretched film made of a polyoxymethylene polymer in which the main part of the main chain is substantially composed of repeating units of oxymethylene groups (-CH ₂ -O-), and the film is measured by the density method. The crystallinity obtained is 75-95%, and
The degree of crystal orientation measured from the edge direction by a line diffraction method is 85 to 95%, and the degree of crystal orientation similarly measured from the end direction is less than the above range,
Furthermore, the Young's modulus in the longitudinal direction is 500 Kg/mm2 or ^more at 20°C, and the Young's modulus in the width direction is 500 Kg/mm2 or more at 20°C.
Base film for magnetic tape less than Kg/mm ² ,
And, there is a magnetic tape in which a magnetic layer is formed on the surface of this magnetic tape base film. (Description of structure) The polyoxyethylene film constituting the present invention has a relatively high molecular weight, for example, a number average molecular weight.
It is derived from polyoxymethylene of 35,000 to 100,000 or more. In the case of a film that requires a high Young's modulus and high dimensional stability, such as the base for a magnetic recording medium of the present invention, polyoxymethylene having a relatively high molecular weight is preferred. In addition, the main part of the main chain is substantially composed of oxymethylene groups (-CH ₂ It can also be applied to polyoxymethylene polymers composed of repeating units of -O-). The above-mentioned polymer is generally suitably formed into a sheet or film by melt molding. for example,
A sheet or film is formed by extrusion and cooling casting by methods such as US Pat. No. 2,936,492. Next, a biaxially stretched film is formed by a simultaneous or sequential biaxial stretching method. By this two-time stretching, the polyoxymethylene is highly oriented and crystallized, and a biaxially stretched polyoxymethylene film having the physical properties of the present invention is formed. The biaxially stretched polyoxymethylene film of the present invention has a crystallinity of 75 to 95% as measured by the density method.
The degree of crystal orientation measured from the edge direction by X-ray diffraction method is 85 to 95%, the degree of crystal orientation similarly measured from the end direction is less than the above range, and the Young's modulus in the longitudinal direction is 85 to 95%. at 20℃
500Kg/mm2 or ^more and Young's modulus in the width direction
Less than 500Kg/ ^mm2 at 20℃. In addition, crystallinity,
The method for measuring the degree of crystal orientation will be described in detail later. By the way, the reason why the above-mentioned differences are made in the degree of crystal orientation in the edge direction and the end direction and in the Young's modulus in the longitudinal direction and the width direction is that the present invention is directed to a magnetic tape. To explain this further, even though it is a base film for magnetic tape, it is ideal to sufficiently stretch both the longitudinal direction and the width direction so that it has excellent physical properties in both directions. However, the stretching in the longitudinal direction and the axial direction are in such a relationship that stretching in one tends to suppress stretching in the other. Therefore, rather than achieving high levels of physical properties in both the longitudinal and width directions, it is easier to improve one of the physical properties to some extent. On the other hand, the length of a magnetic tape is extremely large compared to its width, and its performance is greatly affected by the longitudinal physical properties of the base film. In other words, in a magnetic tape, if the physical properties of the base film in the longitudinal direction are excellent, it is easy to obtain excellent performance as a magnetic tape, and even if the physical properties of the base film in the width direction are somewhat inferior, the performance of the magnetic tape will be improved. It is difficult to have a large impact on the Therefore, in the present invention, the degree of crystal orientation in the edge direction and the end direction and the Young's modulus in the longitudinal direction and the width direction are made different as described above, and the physical properties in the longitudinal direction, which tend to have a large influence, are made higher. This makes it easier to obtain excellent magnetic tapes. The present invention does not particularly limit the method for producing a biaxially stretched polyoxymethylene film having the physical properties of the present invention, but for example, as a preferred example, the method described in detail with the invention previously filed by the present inventors is It is possible to apply methods such as That is, the first manufacturing method is to _roll the melted and solidified raw sheet or _film to Thickness t of film or sheet: After rolling in the longitudinal direction until the thickness of the film or sheet after rolling is reached, it is stretched in the transverse direction by 5 times or more, and then in the longitudinal direction by 5 (1-γ) times or more. This is a method of stretching. The second manufacturing method is to stretch the melted and solidified raw sheet or film in one direction (pre-stretching), and then measure the temperature of the sheet or film using a working calorimeter. Above a temperature close to 30℃ from the peak temperature of the crystal melting curve,
This is a method in which the temperature is maintained at a temperature 5° C. higher than the peak temperature or less, and then the second stage stretching is performed in a direction perpendicular to the direction of the first stage stretching. And this second
In the method described above, it is one of the preferred embodiments that the original fabric is stretched 5 times or more in the above-mentioned first-stage stretching and second-stage stretching. Further, a method in which this second method is combined with the above-mentioned first method is also one of the preferred embodiments. An example of the manufacturing process will be explained in detail with reference to FIG. The method illustrated here is a method in which the second manufacturing method and the first manufacturing method are combined. The polyoxymethylene that has exited the extruder 1 is transferred to the cooling roll 2.
A cooled original fabric is formed. Next, this original fabric is introduced into a rolling mill 3 and rolled. Next, the rolled original fabric is guided to a horizontal stretching machine 4. Transverse stretching is usually performed using a tenter. After being preheated to the stretching temperature at 4', it is laterally stretched at 4''. 4 is a temperature holding zone. Pinch rolls 5 and 6 provided in this zone are used to fix the film after the lateral stretching. During this time, it is also possible to slit the edges of the film.Then, after being preheated to the subsequent stretching temperature by rolls 7, it is longitudinally stretched by stretching rolls 8 and 9.Stretching rolls 8 and 9 The rotational speeds of are set to V ₁ and V _2, respectively, and the longitudinal stretching ratio is determined by this speed ratio V ₂ /V _1. After that, it is cooled by cooling rolls 10 and 11, and then rolled up by 12. Although not shown in the figure, the longitudinally stretched film is heat treated as necessary before being cooled to improve thermal stability, etc. In order to further improve runnability and image stability, it is necessary to use a base that has particularly good Young's modulus and dimensional stability.As for Young's modulus, the thinner the base, the higher the Young's modulus. On the other hand, if a base with a high Young's modulus is used, it will be possible to make the wall thinner than the current level, and the requirement will be extremely large. Rate is 500Kg/ ^mm2 at 20℃
or more, preferably 700 Kg/mm ² or more. In this case, it is also possible to reduce the thickness of the base to 6μ or less. To further improve dimensional stability, the longitudinal thermal expansion coefficient should be -2×10 ^-4 to 2× in the range of 20 to 100°C.
It is preferably within the range of 10 ^-4 mm/(mm·°C); if it exceeds this range, problems are likely to occur due to environmental changes, especially temperature changes. Since the film of the present invention has a high degree of crystallinity, it can sufficiently meet the requirements for dimensional stability. The biaxially stretched polyoxymethylene film of the present invention satisfies the above-mentioned required characteristics as a base film for magnetic tape, and provides an extremely excellent base. Furthermore, the film of the present invention has a higher degree of crystallinity than conventional films. Due to this feature of high crystallinity, it also has more excellent features. For example, there is little decrease in strength, rigidity, etc. due to temperature rise, and heat shrinkage rate etc. can be kept low. Also, if it is for a short time,
Can be used up to nearly 150℃. In known magnetic layer formation methods, such as coating methods and plating methods, it is relatively rare for the tape to be placed in an extremely high temperature environment during the formation process, but this is due to the limited conditions set by the base film. When using the film of the present invention, it is possible to take full advantage of its features for the above-mentioned reasons. For example, productivity can be significantly increased by raising the temperature of the coater. Furthermore, moisture absorption dimensional stability is important for a magnetic tape base. That is, the water absorption rate of the film is required to be as low as possible. Specifically, it is preferable that the equilibrium water absorption rate (24 hours at 20° C. in water) is 0.5% or less. Due to its high crystallinity, the film of the present invention can keep its crystallinity to an extremely low value, and can also provide a base with an extremely low water absorption of 0.2 to 0.3% or less. Various known methods can be used to form the magnetic layer on the film. That is, powders of γ-Fe ₂ O ₃ , Cr ₂ O ₃ , Co-doped iron oxide, metals such as Fe, Ni, Co, and alloys thereof are mixed with appropriate additives, polymeric binders, and solvents. In addition, there is a coated magnetic tape that is prepared as a solution and applied. Polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate polymers, polyamides, epoxy resins, polyurethane resins, silicone resins, and mixtures thereof are used as the polymer binder, and coating methods include gravure roll method and reverse roll method. method, doctor knife method is used, and furthermore, orientation of the magnetic material and calendering are performed. It is also possible to produce a magnetic layer on the film of the present invention by a plating method. Furthermore, as a relatively new method of forming a magnetic layer, the magnetic layer is formed by sputtering a predetermined metal.
By methods such as vapor deposition and ion plating,
A method of forming it directly on the base can also be adopted. Incidentally, the degree of crystallinity and degree of crystal orientation in the present invention are measured as follows. Crystallinity The density (d) of the film was measured using a solution consisting of normal heptane/carbon tetrachloride at 23°C by the density gradient piping method, and was calculated using the formula: D=dc(d-da)/d(dc-ca)× Calculate crystallinity (D) by 100 (%). where dc is 1.506 g/cc, the theoretical density of a fully crystallized polymer, and da is 1.25 g/cc
is the density of the completely amorphous polymer. Degree of Crystal Orientation For each sample, a rectangular molded product with a thickness of 2 mm, a width of 1 mm, and a length of 10 mm was produced with the stretching directions aligned. Cyanoacrylate adhesive was used to fix each film during molding. Next, this molded product is placed at the edge or end of the film on a universal sample stand (rotating sample stand) manufactured by Shimadzu Corporation.
It was installed so that X-rays could enter from any direction. The direction of the sample is shown in Figure 2. The degree of crystal orientation in the longitudinal direction can be obtained from the measured value in the edge direction, and the degree of crystal orientation in the width direction can be obtained from the measured value in the end direction. The X-ray generator used was an XD-3A model manufactured by Shimadzu Corporation, and the X-rays were passed through a Ni filter at 30 KV and 28 mA.
Cu-Kα radiation was used as the X-ray source. The goniometer used was a model XG-108R manufactured by Shimadzu Corporation, which was attached to the rotating sample stand. The slit type has a receiving slit of 2mmφ and a scattering slit of 1mmφ.
It was adopted. Next, the diffraction angle was set to the (100) plane of polyoshimethylene (2θ = 22° to 23.5°), and the X-rays were incident from the edge direction and end direction, and the rotation speed was 4°/min. The sample stage was rotated twice and the diffraction intensity of the (100) plane was scanned in the azimuthal direction. The chart speed of the recorder is
It was 10mm/min. An example of the results obtained by this measurement is shown in FIG. Next, a method for calculating the degree of crystal orientation will be explained with reference to the drawings. Azimuth
For the 90° peak, the peak intensity I from the background is determined, and then the width (half width) W of the peak, which is the intensity I/2, is determined. Note that the background should be determined prior to measurement. Next, the degree of crystal orientation A was calculated using the following formula. A=180-W/180×100 (%) As described above, the base film obtained by the present invention not only makes it possible to obtain thin magnetic tapes that are difficult to produce with conventional ones, but also provides Due to its high Young's modulus, high dimensional stability, and low water absorption, magnetic tape suffers very little damage from deformation of recorded signals or buckling of edges when made into a tape, and is resistant to relatively high temperature thermal history. It has the advantage that troubles such as deformation of the recorded signal, skew changes, and loss of control occur even when the recorded signal is changed, and it can provide an excellent base. The present invention will be explained below with reference to Examples. Example 1 Pellet-like polyoxymethylene homopolymer having a number average molecular weight of about 63,000 is extruded from a slit die at a temperature of 200°C, rapidly cooled with a casting roll heated to 120°C, and a polyoxymethylene sheet with a thickness of 600μ and a width of 150mm is obtained. I got it. Next, this sheet was rolled using a rolling mill at a temperature of 100° C., a reduction ratio of 0.5, and a rolling ratio of 2 times. Next, this rolled sheet is introduced into a biaxial stretching machine, and the stretching temperature is 175-180°C.
The thickness is obtained by biaxially stretching the original sheet at a horizontal stretching ratio of 5.5 times and a longitudinal stretching ratio of 9 times.
A 12μ biaxially stretched polyoxymethylene film was obtained. Table 1 shows the crystallinity, crystal orientation, mechanical properties, and other properties of the film thus obtained. Next, a magnetic tape for video was prepared by coating the stretched film with a magnetic paint having the following composition to a thickness of 5 μm. Composition of magnetic paint γ-Fe ₂ O ₃ powder 22 parts by weight Soybean lecithin 0.5 parts by weight Nitrocellulose 1.5 parts by weight Polyurethane 9.0 parts by weight Methyl isobutyl ketone 50 parts by weight Toluene 17 parts by weight Next, this tape was applied to a helical scan type commercially available video tape. Tape recorder (Matsushita Electric, NV-
350), the running conditions and image stability were measured, and the results shown in Table 1 were obtained. In addition, in Table 1, tape skew a (unit: μsec)
means that a tape with a vertical line image recorded at 20°C and 60% relative humidity is left at 80°C for 24 hours, then returned to room temperature, and immediately played back to determine the relationship between the vertical line image and the vertical reference line at the bottom of the TV image. Tape skew b (unit: .mu.sec) is a value measured in the same manner at room temperature after leaving a recorded tape at 40.degree. C. and 80% relative humidity for 24 hours. The coefficient of thermal expansion is a value determined from the slope of elongation measured at a heating rate of 2° C./min in the range of 20° C. to 100° C. under a load of 1 gr/5 mm width. Comparative Example 1 The pelleted polyoxymethylene used in Example 1 was extruded from a circular die at a temperature of 200°C.
A tube-shaped polyoxymethylene film with a thickness of 15 μm was obtained by an inflation molding method. The crystallinity, crystal orientation, mechanical properties, and other properties of this film are compared with those of Example 1 and are shown in Table 1. Next, the same magnetic paint as in Example 1 was applied, and the running condition and image stability were measured in the same manner. The results are shown in Table 1. The results in Table 1 show that the film of the present invention has extremely excellent performance as a base film for magnetic tape.

[Table] Example 2 The video magnetic tape obtained in Example 1 was
After heating without tension for 5 minutes at ℃, Example 1
As a result of measuring the skew in the same manner as above, it was found that the skew was quite small at 10 μsec, indicating that the base film of the present invention can withstand considerably high temperatures for a short period of time.
Further, when similar measurements were made on the tape obtained in Comparative Example 1, the skew was as large as 20 μsec or more. Comparative Example 2 A magnetic paint was applied to a biaxially oriented polyethylene terephthalate film having a thickness of 9 μm in the same manner as in Example 1 to produce a video magnetic tape. It was found that the skew after heating this tape at 150° C. for 5 minutes without tension was so large that it could not be measured, making it impractical.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of the method for manufacturing the base film for magnetic tape of the present invention; FIG. 2 is an explanatory diagram showing the direction of a sample for measuring the degree of crystal orientation by X-ray diffraction FIG. 3 is an explanatory diagram for showing a method for calculating the degree of crystal orientation. 1... Extruder, 2... Cooling roll, 3... Rolling machine, 4... Lateral stretching machine, 4'... Preheating zone, 4''...
...Stretching zone, 4...Temperature holding zone, 5, 6
...Pinch roll, 7...Heating roll, 8,9...
...Stretching roll, 10, 11...Cooling roll, 12
...Makidori roll.

Claims (1)

[Scope of Claims] 1. The main part of the main chain is substantially oxymethylene group (-
It is a biaxially stretched film made of a polyoxymethylene polymer composed of repeating units of CH ₂ -O-), and has a crystallinity of 75 to
95%, the degree of crystal orientation measured from the edge direction by X-ray diffraction method is 85 to 95%, and the degree of crystal orientation similarly measured from the end direction is less than the above range, and furthermore, the degree of crystal orientation measured from the end direction is 85 to 95%. A base film for magnetic tape having a Young's modulus of 500 Kg/mm ² or more at 20°C and a Young's modulus in the width direction of less than 500 Kg/mm ² at 20°C. 2 The thermal expansion coefficient in the longitudinal direction is in the range of -2 × 10 ^-4 to 2 × 10 ^-4 mm/(mm・℃) in the region of 20 to 100℃, and the equilibrium water absorption rate (24 hours at 20℃ in water) ) is 0.5%
A base film for magnetic tape according to claim 1, which is as follows. 3 The main part of the main chain is substantially an oxymethylene group (-
It is a biaxially stretched film made of a polyoxymethylene polymer composed of repeating units of CH ₂ -O-), and has a crystallinity of 75 to
95%, the degree of crystal orientation measured from the edge direction by X-ray diffraction method is 85 to 95%, and the degree of crystal orientation similarly measured from the end direction is less than the above range, and furthermore, the degree of crystal orientation measured from the end direction is 85 to 95%. A magnetic tape having a magnetic layer formed on the surface of a base film for a magnetic tape, which has a Young's modulus of 500 Kg/mm ² or more at 20°C and a Young's modulus in the width direction of less than 500 Kg/mm ² at 20°C. 4 The longitudinal thermal expansion coefficient of the base film for magnetic tape is -2×10 ^-4 to 2 in the range of 20 to 100°C.
×10 ^-4 mm/(mm・℃), and the equilibrium water absorption rate of the base film for magnetic tape (20℃, underwater
24 hours) is 0.5% or less
Magnetic tape described in section.